Method of and apparatus for use in producing a three-dimensional model of a piece of terrain

ABSTRACT

Method of and apparatus for producing a three-dimensional model of a piece of terrain wherein a plan having contour lines, and a block of machineable material, are traversed in unison past a cursor and a motor-driven shaper element respectively, and the height of the shaper element above the block is controlled by moving a control member to bring the appropriate graduation of a height scale displayed in proximity to the plan and cursor into coincidence with a contour line as the latter passes the cursor during traverse, there being an operative connection between the control member and a height adjustment means for the shaping element. Alternatively the ratio of longitudinal traverse increment to height increment may be preset by operation of key switches each corresponding to a particular graduation on a modified stationary scale extending lengthwise of the direction of longitudinal traverse on both sides of a viewing point.

United States Patent 1,907,250 5/l933 Shaver Inventor Norman Thomas Sanders Green Ridges, Mappleborough Green,

Studley, England Appl. No. 834,453 Filed June 18, 1969 Patented Oct. 19, 1971 Priority June 18, 1968 Great Britain 28961/68 METHOD OF AND APPARATUS FOR USE IN PRODUCING A THREE-DIMENSIONAL MODEL Primary Examiner-Gil Weidenfeld Atl0rneyA. Yates Dowell ABSTRACT: Method of and apparatus for producing a threedimensional model of a piece of terrain wherein a plan having contour lines, and a block of machineable material, are traversed in unison past a cursor and a motor-driven shaper element respectively, and the height of the shaper element above the block is controlled by moving a control member to bring the appropriate graduation of a height scale displayed in proximity to the plan and cursor into coincidence with a contour line as the latter passes the cursor during traverse. there being an operative connection between the control member and a height adjustment means for the shaping element. Alternatively the ratio of longitudinal traverse increment to height increment may be preset by operation of key switches each corresponding to a particular graduation on a modified stationary scale extending lengthwise of the direction of longitudinal traverse on both sides of a viewing point.

PAIENTEDHBT 19 Ian I 3.613501 sum 5 n? 7 v I LONGITUDINRL x (renusveesa) METHOD OF AND APPARATUS FOR USE IN PRODUCING A THREE-DIMENSIONAL MODEL OF A PIECE OF TERRAIN BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method of and apparatus for producing a three-dimensional model of a piece of terrain in respect of which a two-dimensional plan is available, such plan bearing contour marks pertaining to respective altitudes relative to a datum which usually is sea level.

The invention has been developed primarily in relation to the production of three-dimensional models of pieces of ter rain in respect of which the available plan contains contour marks in the form of contour lines. Such contour lines are either all marked on the plan with a figure of the altitude which they represent, or, in certain cases where the slope of the ground is steep, not all of the contour lines are so marked. In that case it is usually indicated on the plan that adjacent contour lines represent altitudes differing by a predetermined value, for example 25 feet, and certain of the contour lines, herein referred to as main contour lines, are thicker, occur at I00 feet intervals of height, and normally are individually marked with their respective altitudes.

It is contemplated, however, that the invention may be applied in cases where the two-dimensional plan available contains contour markings in a form other than lines, for example in the form of zones identified by different colors. In such cases, as will hereinafter appear, the three-dimensional model produced cannot conform in accuracy to that produced where the contour marks are in the fonn of lines, but nevertheless may still represent with a fair degree of approximation the relief of the piece of terrain concerned.

SUMMARY OF THE INVENTION According to one aspect of the invention, a method of producing a three-dimensional model of a piece of terrain bearing contour marks representative of respective altitudes, comprises the steps of, displaying in such mutual proximity to each other as to admit of concurrent viewing, a showing of, a cursor means defining a viewing point, at least a portion of said plan, indicia extending along a line of approach on said portion of said plan leading to said viewing point and providing data for determining proper height adjustment of a shaping means for shaping a model blank, effecting scanning along a scanning path (herein called the primary scanning path) between said plan and said cursor means to cause said portion of said plan to pass said viewing point, viewing at least one of the contour marks intersecting said line of approach, effecting relative scanning along a further scanning path (herein called the secondary scanning path) systematically related to the primary scanning path between said model blank and said shaping means, and adjusting the height of said shaping means relatively to said model blank in conformity with said data to form a surface on said model blank corresponding at least approximately to that represented on said plan by said contour marks.

It is to be understood that the expression cursor means is to be deemed to include any means for identifying a particular position along the primary scanning path, and includes graticule means, and means for causing a light spot, shadow, or other image to be formed on the plan. Further, it is to be understood that the term "height" used in relation to the adjustment of the shaping means relative to the surface of the model blank is a matter of convenience, and that the surface concerned need not necessarily be disposed in a horizontal plane, or approximately horizontal plane, and that for such other positions of said surface, the term "height" is to be deemed to include movement of the shaping means toward and away from said surface.

Instead of displaying an indication of the height of the shaping means in proximity to the cursor means, there may be displayed in proximity to the cursor element and the portion of the plan adjacent thereto, or to images of said cursor means and plan portion, a series of graduation marks spaced apart along the primary scanning path, and each pertaining to a respective ratio of height-adjustment increment to traverse increment along said primary scanning path, graduation marks situated at respectively greater distances from the cursor means pertaining to successively smaller ratios, primary scanning and the height adjustment in this case being effected by way of a series of incremental traverses of the plan means relatively to the cursor means along the primary scanning path, accompanied by corresponding incremental adjustments of height selected by the person carrying out the method in conformity with the particular graduation mark registered with, or immediately adjacent to, a contour mark of identical numerical value intersecting with the primary scanning path on the approach side of the cursor means. The contour mark will ordinarily be that which is nearest to the cursor means on the approach side thereof, but could be another selected contour mark, e.g., every alternate contour mark.

Further, according to the invention, there is provided an apparatus for use in producing a three-dimensional model of a piece of terrain comprising plan support means for supporting a plan of the terrain bearing contour marks representing respective altitudes, work support means for supporting a model blank, cursor means associated operatively with said plan support means and defining a viewing point on said plan, shaping means associated operatively with said work support means for acting on said model blank to form a surface thereon presenting, at each position thereof, a height or thickness of said material representative of a corresponding altitude on said plan, scanning means for effecting corresponding relative scanning on the one hand between said plan support means and said cursor means and on the other hand between said work support means and said shaping means, height-control means adjustable into a plurality of different setting pertaining to respective altitudes, height-adjusting means for determining the height of said shaping means relatively to said work support means and operatively associated with said height-control means for control thereby to set said shaping means to a proper height for forming a surface on said model blank corresponding in relief at least approximately to that represented on said plan by said contour marks, and means for displaying in mutual proximity a showing of, said viewing point, at least that portion of said plan which in consequence of said relative scanning is in a line of approach to said viewing point, and indicia extending along said line of approach and by which correlation with at least one of said contour marks intersecting said line provide data for proper setting of said height-control means.

In one form of the apparatus said means for displaying indicia extending along said line of approach may comprise means for presenting a plurality of graduation marks spaced apart lengthwise of said line of approach and defining a height scale, means being provided for moving said height scale in a direction lengthwise of the line of approach to enable a selected graduation mark to be registered with said viewing point coincident with the time of arrival of a selected contour mark thereat, and means being provided forming an operative connection between said height scale and said height-control means for positioning said height scale longitudinally of said line of approach in conformity with the setting of said heightcontrol means.

In an alternative arrangement of the apparatus, however, the height-control means may include means for generating a plurality of outputs representing respectively different values of height increment and scanning traverse increment ratios, and said means for displaying indicia extending along said line of approach may present a series of graduation marks representing said different ratios respectively, and said heightcontrol means may include manually operable control means settable with selectively to provide an output representing selected one of said ratios whereby an operator can select the ratio indicated by at least approximate coincidence between one of said graduation marks on said line of approach, and a selected contour mark intersecting said line of approach. The height-control means may include a keyboard or the like structure including a plurality of manually operable key elements and means for indicating the particular height to scanning traverse increment ratios to which they relate respectively. With this arrangement the user operates the key element which pertains to the graduation mark on the line of approach which is in register with, or most nearly in register with, the contour mark nearest the cursor means and which intersects the line of approach.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings illustrating em bodiments of the apparatus for carrying out the method of the invention and wherein:

FIG. 1 is a diagrammatic perspective view of one embodiment of the apparatus;

FIG. 2 is a fragmentary plan view of the plan support with a plan mounted thereon and showing a typical relationship between a cursor and a height scale forming part of a heightcontrol means;

FIG. 3 is a perspective view of a constructional embodiment of the apparatus generally similar to that illustrated diagrammatically in FIG. 1 (optical components of the display means, however, being omitted for clarity);

FIG. 4 is a fragmentary view in front elevation of the lower end portion of the shaping element of the apparatus;

FIG. 5 is a view in cross section of the shaping element on the line 5-5 of FIG. 4;

FIG. 6 is a diagrammatic view of another embodiment of apparatus;

FIG. 7 is a fragmentary plan view on an enlarged scale of a portion of a plan and cursor element utilized in the apparatus of FIG. 6;

FIG. 8 is a fragmentary end view showing the profile of a model blank after the latter has been shaped initially, and illustrating the operation of blending or smoothing the surface to remove ridges and valleys;

FIG. 9 is a diagrammatic view illustrating a profile of a model blank in front elevation, such model blank having been produced by the method described with reference to FIGS. 6, 7 or 10 and showing the operation of blending or smoothing the surface in a direction longitudinally of the primary scanning path; and

FIG. 10 is a schematic circuit diagram of another embodiment of apparatus for carrying out the method of the invention and in which means are provided for recording data in digital form relative to traverse and height and for utilizing the recorded data subsequently to control operation of the apparatus.

DETAILED DESCRIPTION Referring firstly to the embodiment of apparatus illustrated diagrammatically in FIG. I, this is designed to operate on the principle that two tables fonning supports respectively for a plan marked with contours, and for a model blank, are subjected to scanning collectively in accordance with a scanning raster consisting of parallel adjacent tracks with incremental traverse in a direction at right angles to the tracks and all in a plane parallel to that presented by the plan.

So far as the plan is concerned, the scanning is effected with respect to a cursor which is fixed to enable the user's eye to be sighted at a given place on the plan coincident with the end of the cursor, and at this place there is also a height scale on transparent material overlying the plan and which the user can move lengthwise of the scale to register a particular height graduation with a contour of corresponding height when this intersects the indicating end of the cursor.

So far as the model blank is concerned, scanning takes place with respect to a motor-driven shaping element for milling or cutting away the material of the model blank down to a height corresponding to that which, at any given instant, is the height of the ground represented on the plan at the point in register with the indicating end of the cursor.

The height of the shaping element is controlled by the position of the height scale and, therefore, on completion of a complete scanning cycle over the entire area of the plan, the model blank is machined in relief to produce a three-dimensional model of the piece of terrain represented by the plan.

The apparatus illustrated diagrammatically forcarrying out this general method comprises two tables 10 and 11 forming supports respectively for a plan 12 and a model blank 13.

The tables I0 and II are coupled to each other, for example by a longitudinal lead screw 14 driven from a motor IS. The increments of scan in a direction at right angles are imparted by lead screws 16 and 17 which are connected by a positive transmission system 18 (which may comprise chain and sprocket drive or toothed belt and recessed pulley elements). The execution of the transverse incremental scan is effected manually by means of an operating arm 19 movable over an indicator plate 20 graduated to enable the magnitude of each incremental movement to be selected in accordance with the quality of the work to be produced.

Above the table 10 and plan 12 is disposed a cursor 21 of transparent material marked with a cursor line 22, the free end of which forms in locating point for the eye. Past the free end of the cursor line 22 is laid a piece of transparent tape 23 which can be moved longitudinally in opposite directions, as indicated by arrow 24, by means of a handwheel 25 forming a height-control member equipped with radially projecting finger pieces 26.

The tape 23 is graduated with marks representing height values. The longitudinal position of the tape is controlled by a drum 27 driven from the handwheel 25 through a gearbox 28 and shaft 29, and the tape afier passing beneath a guide pulley 30 is wound onto a further drum 31 coaxial with, and fixed to, a transfer drum 32. From the transfer drum a further tape 33 is wound onto an input drum 34 of a height adjustment means 35 including a pinion 36 driven from the input drum 34 and meshing with a vertical rack 37.

Above the table II and model blank 13 is disposed a motor 38 having a vertical spindle driving a shaping element 39.

A portion of the plan in the vicinity of the free indicating end of the cursor line 22, together with a portion of the cursor and a portion of the tape 23 bearing the height scale, is displayed in magnified form on a screen 40 by an optical system 41. The optical system 41 comprises a source of illumination such as two lamps 42 disposed beneath a masking plate which at its underside may be formed as a reflector to throw light onto the plan. A magnifying lens assembly 43 and mirrors 44 and 45 form an image on the screen 40. The parts of the image are designated by numerals corresponding to the objects from which they are derived with the suffix a.

Referring to FIG. 2 which illustrates the manner of carrying out the invention using, for example, the apparatus of FIG. I, it will be noted that the plan 12 is shown as including contour lines representing a hill. Only the main contour lines at I00 feet intervals are identified numerically and the intervening contour lines represent increments of 25 feet.

Operation of the scanning motor 15 will cause the plan to travel at a speed selected by the operator, movement taking place in the direction of the arrow 47. Under the conditions illustrated in FIG. 2 it will be noted that the free end of the cursor line 22 is intersected by the 200 feet contour and the tape 23 has been moved by operation of the handwheel 25 into a position at which the 200 feet graduation on the height scale of the tape is in coincidence with the cursor line. The next contour which will arrive in intersecting relation with the free end of the cursor line 22 is the I75 feet contour and accordingly the operator will require to move the tape longitudinally to bring the feet graduation into coincidence with the cursor line 22 by the time the 175 feet contour has arrived at this position.

The arrow 24 signifies that the tape 23 can, of course, be moved in both directions, one direction being appropriate to ascending ground and the other to descending ground.

On completion of a complete longitudinal traverse of the plan a further scan takes place along a parallel and adjacent track by operating the lever arm 19 to a new position, for example moving it through a right angle may correspond to the finest transverse scan provided, and it may selectively be moved through 180', 270', or a complete revolution, or indeed any other angular increments identifiable by markings on the plate 20.

The image formed on the screen 40 of the plan, cursor and height scale by the lens assembly 43 and the mirrors 44 and 45 transforms the horizontal longitudinal movement to a vertical movement (the mirror 44 inclining upwardly from right to left as viewed in front elevation, and the mirror 45 inclining from right to left in a direction from the rear to the front of the apparatus). The gearing in the gearbox 28 is so arranged that upward movement in an arcuate direction of the ends of the finger pieces 26 produces upward movement of the height scale image on the screen and vice versa.

The movement of the tape 23 is transmitted to the motor 38 and shaping element 39 and accordingly the model blank is machined to the required height at each position. The drum assembly 31, 32 provides the facility for changing the height scale. As illustrated there is a magnification of the height scale due to the larger diameter of the transfer drum 32 compared with the drum 3]. One or both of these two drums would be removably mounted on a spindle.

The tapes would be positively anchored to the drums 27, 31, 32 and 34 and means not illustrated in FIG. I are provided for maintaining appropriate tension in the tapes.

The embodiment of apparatus illustrated diagrammatically in FIG. I is shown in constructional form in FIG. 3 wherein parts corresponding to those already described are designated by like numerals of reference. In this embodiment components of the optical system for forming images of the plan, cursor, and height scale of the tape on the screen 40 are omitted for simplicity. The manually operable lever arm 19 and associated plate 20 are also omitted.

Reference will be made, therefore, briefly to the parts illustrated in FIG. 3 and not already described. The tables and II are carried by respective subframes movable on, and longitudinally of, respective guide rails 50 and 51 preferably through the intermediary of rollers such as are seen at 52 and which may be mounted through the intennediary of ball or roller hearings on the subframes.

Each pair of guide rails 50 and 51 can be traversed laterally by lead screws 16 and 17 respectively. The subframes of the two tables 10 and 11 are effectively coupled for longitudinal movement by means of a tubular transmission shaft 14a driven from motor through the intermediary of a reduction gear 65 and a chain and sprocket or a toothed belt and pulley gear 654. The gear 65 which may, if desired, be adjustable steplessly or in increments under the control of a manually operable control member such as knob 66. At the ends of the shaft 14a further chain and sprocket or toothed belt and pulley gears 14b, 14c connected thereto through universal couplings drive lead screws 14d, 14 for the two tables 10 and 11. The ratio of longitudinal traverse of one table relative to the other can be varied by changing the ratios of either the gear 141: or 14c, or both.

A supporting structure in the form of an openwork frame indicated generally at 53 supports the guide rails 50 and 51, the latter being connected to each other at their ends by transverse members 54 and 5 respectively, the two outermost transverse members being equipped with rollers 56 and 57 running on transverse rails 58, 59 of the main frame 53.

The height-adjustment means 35 is supported on an upward extension 60 of the main frame and includes an upwardly extending guideway 61 in which the rack bar 37 is mounted for vertical movement, counterbalance being provided for the weight of this bar and the motor 38 in the form of a counter weight (not shown) attached to a cable 62 passing over guide pulleys 63.

The optical system 41 is contained in a housing 64 open at its underside and capable of being hinged about a horizontal axis extending transversely to the length of the main frame 53 adjacent to the lower corner of the housing to an open position in which access can be obtained to the components of the optical system as required.

Referring specifically to the shaping element 39, this is illustrated in more detail in FIGS. 4 and 5 and, as viewed in plan cross section, may be of approximately D-form having a flat plane face 67 and an arcuate face 68 which, having regard to the direction of rotation indicated by the arrow 69, is relieved or cut away over a portion of its length 70 immediately on the trailing side of the cutting edge 71 formed at the intersection with the plane face 67. The length of the shaping element is sufficient to enable it to penetrate from the top surface of the model blank to the depth representing the lowest level of terrain and typically lengths of 1 inch to 6 inches may be employed. As viewed in front elevation in FIG. 4, it will be noted that the lower extremity of the shaping element is of arcuate form, as shown by the boundary 72, and typically this may have a radius of curvature of three sixty-fourths inch or thereabout depending upon the fineness" with which machining is required to be carried out. A smaller radius of curvature would be employed in cases where the steepness of the slope to be cut on the model blank requires this and a larger radius of curvature would be appropriate in cases where the relief of the terrain did not include any steeply sloping portions.

Removal of material from the surface of the model blank takes place by way of a series of parallel traverses and the centers of these are necessarily a finite distance apart, so that it is desirable that the radius of curvature of the boundary 72 should not be greater than that required to ensure that the steepest slope required to be presented on the finished model can be formed. Formation of ridges may be reduced by adopting an appropriately small increment of lateral traverse.

it will be understood that various modifications may be made in the form of apparatus and manner of carrying out the method, of which the following are specifically mentioned although not exhaustive of those which might be made.

Firstly, as to relative traverse between the cursor element and the support for the plan, it would be within the scope of the invention to utilize a mode of scanning other than traverse along mutually perpendicular paths to provide a parallel track-scanning raster as described. Thus, for example, a spiral scanning path, of which the convolutions are of circular or some other shape, for example square or rectangular, could be employed.

Whatever the form of the scan the speed of scanning may be adjusted under the control of the operator. Thus means may be provided for selecting a plurality of preset rates of scan by means of a speed controller associated with motor 15, or such controller may be adapted to vary the speed of the motor steplessly, in either case by means of a manually operable control member. The operator is thus enabled to reduce the speed of scan over portions of the scanning path which require extensive adjustment of the height of the shaping element, for example when the scanning path is traversing a portion of the plan representing a steep hill or valley, while the speed of scan can be increased for portions of the scanning path which traverse respective portions of the plan representing uniformly sloping or relatively flat parts of the terrain.

The coupling between the two tables 10 and 11 need not necessarily provide a 1:1 ratio as to the magnitude of scanning displacements. The coupling could include a variable ratio gear enabling either the longitudinal scan component or transverse scan component to be magnified or diminished in respect of the table ll, compared with those applied to the table 10 if desired.

Further, the displayed indication of height on the screen 40 may, but need not necessarily. include numerical indication of the height in respect of each graduation mark displayed. In practice numerical indication is conveniently applied to graduation marks corresponding to the main contour lines, that is at I feet intervals, and graduation marks corresponding to 25 feet intervals, are smaller size and unmarked.

Further, while it is preferred that adjustment of the heightadjustment means 35 be carried out steplessly and by operation of the manually operable member 25, height adjustment in increments would be within the scope of the invention and could be carried out by power energized means brought into operation or controlled manually. For example, a height-adjusting electric motor could be used to rotate a pinion 36, and a further motor rotating in corresponding incremental steps would be used to adjust the position of the tape 23 rather than the tape itself forming a mechanical means for transmitting movement to the height-adjusting means 35.

An alternative embodiment of apparatus is illustrated diagrammatically in FIG. 6.

This is intended for carrying out the method of the invention in a somewhat different manner.

In this case, as illustrated in FIG. 7, a fixed cursor element 12] is provided having a graticule line 122 and adjacent to the free end of this line the cursor element is marked with graduations which typically may be numbered 1 to 8 and spaced apart equidistantly along the edge l22b of the cursor element at right angles to the line 122. Each graduation represents a certain ratio of height increment to traverse increment.

Traverse of the plan past the cursor element is carried out in a direction parallel to the edge l2lb and in accordance with this manner of carrying out the method, the operator sets the increment of adjustment to be applied by the height-adjustment motor and the increment of traverse to be applied by the longitudinal traverse motor to a value appropriate to that represented by the contour line which will next come into register with the graticule line 122.

For example, successive contour lines are indicated at A, B, C and it will be noted that on the approach side, that is to say on the left-hand side of the graticule line 122, contour B intersects the edge 121b of the cursor element in register with graduation mark No. 5. By the time the left-hand side of the loop presented by contourline A has reached the graticule line 122, however, contour line B would be in register or approximate register, with graduation mark 3. The operator would be able to discern from the altitude markings on the contour lines whether the terrain was ascending or descending and would then operate appropriate controls to set a height to traverse ratio which would cause the support for the plan to be traversed in the direction of the arrow 147, and would concurrently bring about an adjustment of the height of the shaping element by an amount representative of the difference between the height designated by contour line A and the height designated by contour line B.

The adjustment of height would be carried out linearly so that the method represents an approximation, in that the shaping element would machine a uniformly descending or uniformly ascending track along a model blank, whereas it will be evident from the contours represented typically in FIG. 7 (assuming these to represent a hill) that the proper adjustment of the shaping element would be firstly a slight rise or maintenance at a fixed height until the other side of the contour A is reached, followed by a descent of the shaping element at an approximately uniform rate corresponding to graduation mark 3 until the time at which contour line 8 comes into register with the graticule line at the zero position.

The ultimate form of the model produced consists along each scanning track of a succession of rectilinear portions which slope upwardly or downwardly, or are level in a direction from one end of the track to the other, and consequently some finishing or correcting operation will, in many cases, require to be carried out after completion of the machining operation.

As seen in FIG. 6, tables and 111 are provided for supporting respectively a plan and a model blank, the latter being shown at 113. An optical system having a screen and arranged above the table 1 10 provides an image 1210 of the cursor element while above the table 111 is provided a shaping element 139 and a drive motor 138 therefor, together with a height-adjustment means 135 similar to that already described except that the pinion 136 is driven by a motor 170.

Scanning of the tables 110 and 111 may be effected in the same manner as in the embodiment illustrated in FIG. 1 and FIG. 3, for example, by means of a longitudinal lead screw 114 driven by a motor 1 15, the means for providing increments of transverse scanning being omitted for simplicity.

Motors and 115 are supplied with respective current pulses.

it is assumed that successive contour lines represent equal increments of height and consequently the current pulses supplied to motor 170 will be of equal duration and magnitude, whereas those supplied to the motor 115 will be of the same durations as those supplied to motor 170 but of difl'erent magnitudes proportional in each case to the distance of the graduation mark intersecting with the next contour to approach the graticule line when the preceding contour mark is in register therewith. This provides for continuous drive by each motor during each increment of adjustment.

The operators control may conveniently comprise a keyboard 17! having a plurality of individual control members such as depressable keys or buttons 172, each pertaining to one of the graduation marks and arranged in a vertical row to occupy positions in that row corresponding to the graduation marks, whereby the operator can readily select the proper key for operation.

Depression of a given key would apply a signal along conductor 176 to a pulse-generating circuit 173 providing a constant magnitude pulse onto the line 174 and a variable magnitude pulse onto the line 175.

Collectively the pulses of current applied to the line 174 represent a current of constant magnitude and the pulses applied to the line 175 represent a current of a varying magnitude. These signals may be applied to the recording head of a tape recorder 177 which, through a suitable control circuit 178, can on playback, utilizing the recording head as a reading head, or using a different reading head, deliver signals to the lines 174 and 175.

Assuming that a means were provided for stopping travel of the tape through the recording head at the end of each current pulse appearing on the line 175 and each corresponding current pulse (if any) on the line 174, the length of tape passing through the recording head would represent distance travelled along the primary scanning path and the intensity of magnetization at any position would represent the altitude, so that the record impressed on the tape is true analogue, subject to the approximation that altitude changes take place in a series of rectilinear portions which may slope either up or down, or may be level instead of accurately representing the curvature (if any) of the ground. As will hereinafter appear, the inaccuracies introduced by the ridges or valleys representing the discontinuity at the junction of each such section can be removed.

If the recording head were so designed that variations in the magnitude of current produced corresponding variations in the width of the magnetized area in the track, then the profile of the boundary of the magnetized area would represent the profile of the terrain. in practice, however, the whole width of a track may be magnetized but to varying degrees of intensity.

In effecting playback it is merely necessary to synchronize travel of the tape through the reading or playback head with movement of the model blank along the model scanning path, the height of the shaper element being automatically adjusted as a function of the width or intensity of magnetization. Any suitable marking signal may be generated and applied to the tape to identify the end of each longitudinal traverse and stop the tape motor so that until a transverse increment of scan is applied by the operator, a further longitudinal traverse recorded on the next scan of tape cannot be applied.

it will be understood that for simplicity the requisite feedback paths from the motors 1 and 170 to the pulse-generating circuit supplying these motors, and which would be provided in accordance with normal practice to ensure stability, have been omitted.

in FIG. 10 there is illustrated schematically a form of apparatus for carrying out the method in accordance with the general principles already described with reference to FIG. 7 but utilizing a digital system for controlling operation of the height motor and longitudinal traverse motor, and incorporating also means for recording the requisite signals in digital form by means of a tape recorder.

in this case the keyboard is provided as before with individual control members such as depressible keys or buttons which may be arranged in a vertical row. Typically there would be eight such keys or buttons corresponding to graduations 1 to 8 for ascending terrain and eight similar keys or buttons corresponding to graduations l to 8 for descending terrain. Of these only Nos. l, 7 and 8 are shown in FIG. 10 designated for ascending terrain and designated for descending terrain.

A constantly operating pulse generator 200 provides positive-going short pulses at a suitably high repetition rate to nine frequency-divider circuits, of which eight are associated respectively with the eight key switches +1 to +8 (and 1 to -8), only three of these being shown at 2010, 207a, and 2080. The ninth frequency-divider circuit is designated 2090.

The key switches +1 to +8 and l to 8 are connected to respective monostable circuits such as +208b, +207b, +201b, -201b, 207b, 208b, all of which furnish square wave pulses when triggered by operation of their associated key switch of constant and equal duration long enough to accommodate the longest pulse group required (namely that furnished by frequency-divider circuit 208a).

Pulses from the frequency-divider circuits are gated with the outputs from the monostable circuits in nine gate circuits such as those indicated 201c, 207c, 208c and 209s. Of the eight gate circuits associated with the key switches only one will be opened at any given time and will feed an output to a driver circuit 216 for driving the longitudinal traverse (X- traverse) motor 215, and hence the plan and model tables 210 and 211, through lead screw means indicated diagrammatically in broken lines at 214.

The output from the ninth frequency-divider circuit 2090 is gated in gate circuit 209a with the output from a monostable circuit 209!) which is operated by an output from a switch 9 linked mechanically with the key switches +l to +8 and l to 8 so as to be operated whenever one of these key switches is operated, the mechanical connection being indicated in broken lines at 90. The output from the switch 9 operates a mark and switch circuit 217 somewhat in advance of the closure of the contacts of the key switches which initiate outputs from the monostable circuits connected thereto, and accordingly a delay circuit 218 is inserted in the connection from the switch 9 to monostable circuit 209b to ensure that the output developed from the latter starts and ends in coincidence with the outputs from the key switch monostable circuits.

The outputs from gate circuit 2090 is fed to a further driver circuit 220 through the intermediary of an inverter circuit 221 which inverts the polarity of the output from the gate circuit 2090 whenever gating occurs through operation of any of the group of positive key switches +1 to +8 by virtue of the connection to the inverter circuit from the monostable circuits associated respectively with this group of key switches.

Accordingly the sign of the output from 221 differs according to whether the key switch operated is in the group +l to +8 or-l to 8.

The driver circuit 220 feeds the height motor 270 to control the height of the shaper motor 238 and hence the contour of the track cut on the model blank 213.

Motors 215 and 270 may adapted to operate stepwise. For example, driving motors similar to those utilized for uniselector switches may be employed, each impulse delivered from the driver circuit advancing the motor by one step, and in the case of the motor 270 the direction of movement being dependent upon the sign of the output from the driver circuit.

The respective division factors for the frequency-divider circuits 201a to 208a are so selected that the number of pulses delivered to driver circuit 216 is proportional to the dimension represented by the graduations l to 8. The division factor in respect of frequency-divider circuit 2090 is selected to enable the steepest slope required to be cut and accordingly the number of pulses delivered in each group from the gate circuit 209c will require to be less than that delivered from gate circuit 201: where gradients of more than 45 to the horizontal are to be represented. The frequency division is in each case by a whole number.

Mark and switch signals developed in circuit 217 are applied respectively to driver circuits 216 and 220 to prepare these for operation for the onset of each pulse group and such driver circuits may, for example, include a monostable input stage which is operated by the mark and switch signal and remains open to allow the driver to operate for the duration of the signal group and thereafter revens to an inoperative state until opened by the next succeeding mark and switch signal. A similar arrangement may be provided in a tape motor control circuit 222 to ensure that the tape motor 223 operates the appropriate tape reel 224 only over an interval starting a short time before each signal group and ending a short time after the end of the pulse delivered by the monostable circuits associated with the key switches.

Signal groups applied to driver circuits 216 and 220 may be recorded on respective tracks of a tape 225 traversed past a recording head. A limit switch 227 operated by either of the tables 210 and 211, or a part moving therewith, furnishes a signal to a traverse motor control circuit 228 controlling the operation of a traverse motor 229 for effecting collective movement of the two tables in a direction (the Y direction) crosswise of the X-traverse direction. The control circuit 228 may develop a mark signal denoting the end of a longitudinal traverse and recorded on a third track of the tape 225. The Y motor control circuit 228 may also supply an inhibiting signal to the tape motor control circuit 222 to prevent any further traverse of the tape until the Y motor 229 has applied an increment of cross traverse to the tables.

A reading head, shown separately for convenience but which may be constituted by the recording head and suitable switch means, provides outputs to enable signals recorded on the tape, including the mark and switch signals from circuit 217 and the mark signal from the circuit 228, to be applied to driver circuits 216 and 220 and to the Y motor control circuit 228 for effecting appropriate movements of the two tables and the height motor in response to passage of the tape past the reading head.

As seen in FIG. 8, both manners of carrying out the method of the invention produce a machined surface on the model blank which contains a plurality of ridges [3a extending in the direction of longitudinal traverse. The method includes the step of blending the surface of the model blank to smooth form by acting on these ridges or discontinuities along each traverse to transport particles in an appropriate manner from one place to another. For example, where the model blank presents only ridges and the height of the model blank along each machined track corresponding to a longitudinal traverse is an accurate analogue of the altitude, transportation of material need only be effected in the direction of the transverse scan. ln this case material may be transported from the ridges into the valleys 13!: between the ridges using a wiping element 13c in the presence of an eroding agent such as a liquid.

To enable this operation to be carried out the material, of which the model blank is made, may consist of particles which can be removed by application of a convenient liquid eroding agent such as water. A particularly suitable material has been found to be hard plaster. A suitable wiping element is one composed of feltor a stiff brush such as a stencil brush moistened with the water. This would be wiped over the surface of the model block in a direction transversely to'the length of the ridges and valleys, as shown by arrow 13d, and material removed from the ridges then settles in the valleys and readheres to the surface of the blank upon drying out, as represented by the full line to the right of the brush.

In the case where the method is carried out in the manner illustrated and described with reference to FIG. 7, the profile of the model longitudinally of the direction of traverse will consist of a succession of rectilinear portions which are level or slope upwardly or downwardly and meet in abrupt ridges or discontinuities. The step of blending the surface in this case is applied to the model blank both transversely, as described with reference to FIG. 8, and longitudinally, as illustrated in FIG. 9.

In this case successive rectilinear portions of the longitudinal profile are shown at 113a with ridges 113] of varying severity at the junctions of these portions and an abrupt concavity at 113g. The ridges and concavity may be smoothed to the form indicated in broken lines by means of a wiping element 113d moved as indicated by the arrow ll3c in the presence of an eroding agent such as has already been mentioned relative to FIG. 8.

The model thus produced can be utilized to form a master from which other models can be produced, for example by means of a rubber mold formed of silicon rubber which will pick up small details in relief.

By this method a very accurate smooth representation of the relief of the terrain is obtained.

A representation of the terrain, but omitting the contour lines, may be applied to the surfaces of models thus produced in any convenient manner, for example, by hand painting or by a photographic printing process. If hand painting is used an image of the representations of the plan may be projected onto the surface of the model and painting may then be effected in accordance with this image.

I claim:

1. Apparatus for use in producing a three-dimensional model of a piece of terrain comprising:

a. plan support means for supporting a plan of the terrain bearing contour marks representing respective altitudes,

b. work support means for supporting a model blank,

c. cursor means associated operatively with said plan support means and defining a viewing point on said plan,

d. shaping means associated operatively with said work support means for acting on said model blank to form a surface thereon presenting, at each position thereof, a height or thickness of said material representative of a corresponding altitude on said plan,

e. scanning means for effecting corresponding relative scanning on the one hand between said plan support means and said cursor means and on the other'hand between said work support means and said shaping means,

f. height-control means adjustable into a plurality of different settings pertaining to respective altitudes,

g. height-adjusting means for determining the height of said shaping means relative to said work support means and operatively associated with said height-control means for control thereby to set said shaping means to a proper height for forming a surface on said model blank corresponding in relief at least approximately to that represented on said plan by said contour marks,

h. and means for displaying in mutual proximity a showing i. said viewing point,

ii. at least that portion of said plan which in consequence of said relative scanning is in a line of approach to said viewing point,

iii. indicia extending along said line of approach and which by correlation with at least one of said contour marks intersecting said line provide data for proper setting of said height-control means.

2. Apparatus according to claim 1 wherein said scanning means comprises:

a. longitudinal scanning means for effecting relative reciprocating movement between said plan support means and said cursor means on the one hand, and between said work support means and said shaping means on the other hand in a direction parallel to one dimension of said plan,

b. transverse scanning means for effecting relative incremental scanning movement in a direction transverse to said dimension between said plan support means and said cursor means on the one hand, and between said work support means and said shaping means on the other hand, whereby relative scanning takes place along a scanning path represented by a succession of parallel tracks collectively forming a raster covering the required area of the plan.

3. Apparatus according to claim 2 wherein at least one of said longitudinal and transverse scanning means includes means for varying the ratio of relative scanning displacement imparted between said work support means and said shaping means to the relative scanning displacement imparted between said plan support means and said cursor means.

4. Apparatus according to claim 1 wherein:

a. said means for displaying indicia extending along said line of approach comprises means for presenting a plurality of graduation marks spaced apart lengthwise of said line of approach and defining a height scale,

b. means are provided for moving said height scale in a direction lengthwise of the line of approach to enable a selected graduation mark to be registered with said viewing point coincident with the time of arrival of a selected contour mark thereat,

c. means are provided forming an operative connection between said height scale and said height-control means for positioning said height scale longitudinally of said line of approach in conformity with the setting of said heightcontrol means.

5. Apparatus according to claim 4 wherein:

a. said means for presenting said graduation marks comprises a strip or sheet element of light-transmitting material,

b. means are provided for mounting said element in superposed relation to said plan,

c. said means forming an operative connection between said height scale and said height-control means includes a cable means connected operatively to a movable output element of said height-control means and to a movable input element of said height-adjustment means, and subjected to longitudinal movement in response to operation of the former,

d. said strip or sheet element of light-transmitting material is included in or connected to said cable means so that at any instant it occupies a position longitudinally of the height scale detennined by the setting of both said heightcontrol means and said height-adjustment means.

6. Apparatus according to claim 4 wherein:

a. said height-control means includes a manually operable control member having at least one finger piece movable in opposite directions along an adjustable path,

b. said display means presents said height scale and said line of approach in an orientation such as to extend generally longitudinally of said adjustment path,

c. said means forming an operative connection between said height scale and said height-control means provides for movement of said height scale in a direction to move a selected graduation mark away from said viewing point and towards said viewing point in response to alternations in the setting of said adustment means.

7. Apparatus according to claim 1 further comprising means for varying the magnitude of the height adjustment of the shaping means produced in response to operation of the height-adjustment means for a given change of setting of the height-control means to enable the steepness of the gradients formed on said surface of said model to conform to those represented by said contour marks on said plan, or to be exaggerated or diminished as required.

8. Apparatus according to claim 1 wherein:

a. said height-control means includes means for generating a plurality of outputs representing respectively different values of height increment and scanning traverse increment ratios,

b. said means for displaying indicia extending along said line of approach presents a series of graduation marks representing said difierent ratios respectively,

c. said height-control means includes manually operable control means settable selectively to provide an output representing a selected one of said ratios whereby an operator can select the ratio indicated by at least approximate coincidence between one of said graduation marks on said line of approach, and a selected contour mark intersecting said line of approach.

9. Apparatus according to claim 1 wherein said manually operable control means comprises a keyboard including a plurality of manually operable key elements and means for indicating the particular height to scanning traverse increment ratios to which they relate respectively.

10. Apparatus according to claim 1 wherein said means for displaying said viewing point, said portion of said plan, and said indicia comprises optical means for forming magnified images thereof.

11. Apparatus according to claim wherein said optical means includes:

a. a housing extending over said cursor means, a portion of said plan adjacent thereto, and said means displaying said indicia,

b. a light source in said housing for illuminating said portion of said plan,

c. a display screen on which said magnified images are formed.

12. Apparatus according to claim 1 wherein:

a. said height-adjustment means includes actuating means responsive to an electrical height signal,

b. said apparatus further includes reading means for generating said signal in response to playback of a record member thereby, and means for feeding said signal to said height-adjustment means,

c. means are provided for correlating playback of said record member and operation of said scanning means whereby said shaping means is set to a proper height relative to said work support for each position of relative scan between said work support and said shaping means.

13. Apparatus according to claim 11 wherein said apparatus further includes recording means including:

a. means for advancing a record member through a recording station in correlation with relative scanning between said plan support means and said cursor means,

b. a recording head at said station for impressing a record on said record member in response to an electrical signal,

7 c. means for generating said electrical signal varying in dependence upon the altitude represented by said contour marks.

14. Apparatus according to claim 11 wherein:

a. said actuating means of said height-adjustment means provides stepless or continuous operation of said heightadjustment means,

b. said reading means provides a height signal which is an analogue of the corresponding altitudes represented by said contour marks.

15. Apparatus according to claim 11 wherein:

a. said actuating means of said height-adjustment means provides stepwise operation of said height-adjustment means,

b. said reading means provides a height signal which digitally represents the altitudes represented by said contour marks.

16. A method of producing a three-dimensional model of a piece of terrain from data provided by a plan of the terrain bearing contour marks representative of respective altitudes, said method comprising the steps of:

a. displaying in such mutual proximity to each other as to admit of concurrent viewing showing of i. a cursor means defining a viewing point ii. at least a portion ofsaid plan iii. indicia extending along a line of approach on said portion of said plan leading to said viewing point and providing data for determining proper height adjustment of a shaping means for shaping a model blank,

b. effecting relative scanning along a primary scanning path between said plan and said cursor means to cause said portion of said plan to pass said viewing point,

c. viewing at least one of the contour marks intersecting said line of approach,

d. effecting relative scanning along a secondary scanning path systematically relating to said primary scanning path between said model blank and said shaping means,

e. positioning at least part of said data in substantial registration with at least one of said contour marks at said viewing point and adjusting the height of said shaping means relative to said model blank in conformity with said data to form a surface on said model blank corresponding at least approximately to that represented on said plan by said contour marks.

17. A method according to claim 16 wherein said indicia provide data as to the present height of the shaping means, and adjustment of the height of said shaping means is effected to bring about at least approximate correspondence between said indicated height and the altitude represented by the contour mark at the time when said mark passes said viewing point.

18. A method according to claim 17 wherein the height is displayed by displaying a succession of graduation marks spaced apart in a direction longitudinally of said line of approach and effecting movement of said graduation marks collectively in correspondence with adjustment of the height of said shaping means to bring the appropriate graduation mark into coincidence with said viewing point.

19. A method according to claim [6 wherein:

a. said indicia comprises a succession of graduation marks spaced apart along said line of approach, each pertaining to a respective ratio of height adjustment to scanning increment, graduation marks situated at respectively greater distances from the viewing point defined by said cursor element pertaining to successively smaller ratios,

b. scanning and height adjustment is effected by way of a series of relative scanning displacements on the one hand between said plan and said cursor means, and on the other hand between said model blank and said shaping means, accompanied in the latter case by such respective corresponding incremental adjustments of the height of said shaping means relative to said surface of said model blank as are detennined by registration or approximate registration between one of said graduation marks and a contour mark of identified numerical value intersecting with said line of approach.

20. A method according to claim 16 comprising the further step of:

a. effecting relative advancement of a record member through a record station in correspondence with distance scanned along said primary scanning path,

b. impressing on said record member data representing the height to which said shaping means are required to be adjusted in accordance with the altitude represented by said viewed contour marks,

c. subsequently controlling relative scanning movement along said model scanning path between said model blank and said shaping means in accordance with advancement of said record member through a reading station,

d. controlling the height of said shaping means with respect to said surface of said model blank in accordance with the data recorded on said record member. 

1. Apparatus for use in producing a three-dimensional model of a piece of terrain comprising: a. plan support means for supporting a plan of the terrain bearing contour marks representing respective altitudes, b. work support means for supporting a model blank, c. cursor means associated operatively with said plan support means and defining a viewing point on said plan, d. shaping means associated operatively with said work support means for acting on said model blank to form a surface thereon presenting, at each position thereof, a height or thickness of said material representative of a corresponding altitude on said plan, e. scanning means for effecting corresponding relative scanning on the one hand between said plan support means and said cursor means and on the other hand between said work support means and said shaping means, f. height-control means adjustable into a plurality of different settings pertaining to respective altitudes, g. height-adjusting means for determining the height of said shaping means relative to said work support means and operatively associated with said height-control means for control thereby to set said shaping means to a proper height for forming a surface on said model blank corresponding in relief at least approximately to that represented on said plan by said contour marks, h. and means for displaying in mutual proximity a showing of: i. said viewing point, ii. at least that portion of said plan which in consequence of said relative scanning is in a line of approach to said viewing point, iii. indicia extending along said line of approach and which by correlation with at least one of said contour marks intersecting said line provide data for proper setting of said height-control means.
 2. Apparatus according to claim 1 wherein said scanning means comprises: a. longitudinal scanning means for effecting relative reciprocating movement between said plan support means and said cursor means on the one hand, and between said work support means and said shaping means on the other hand in a direction parallel to one dimension of said plan, b. transverse scanning means for effecting relative incremental scanning movemEnt in a direction transverse to said dimension between said plan support means and said cursor means on the one hand, and between said work support means and said shaping means on the other hand, whereby relative scanning takes place along a scanning path represented by a succession of parallel tracks collectively forming a raster covering the required area of the plan.
 3. Apparatus according to claim 2 wherein at least one of said longitudinal and transverse scanning means includes means for varying the ratio of relative scanning displacement imparted between said work support means and said shaping means to the relative scanning displacement imparted between said plan support means and said cursor means.
 4. Apparatus according to claim 1 wherein: a. said means for displaying indicia extending along said line of approach comprises means for presenting a plurality of graduation marks spaced apart lengthwise of said line of approach and defining a height scale, b. means are provided for moving said height scale in a direction lengthwise of the line of approach to enable a selected graduation mark to be registered with said viewing point coincident with the time of arrival of a selected contour mark thereat, c. means are provided forming an operative connection between said height scale and said height-control means for positioning said height scale longitudinally of said line of approach in conformity with the setting of said height-control means.
 5. Apparatus according to claim 4 wherein: a. said means for presenting said graduation marks comprises a strip or sheet element of light-transmitting material, b. means are provided for mounting said element in superposed relation to said plan, c. said means forming an operative connection between said height scale and said height-control means includes a cable means connected operatively to a movable output element of said height-control means and to a movable input element of said height-adjustment means, and subjected to longitudinal movement in response to operation of the former, d. said strip or sheet element of light-transmitting material is included in or connected to said cable means so that at any instant it occupies a position longitudinally of the height scale determined by the setting of both said height-control means and said height-adjustment means.
 6. Apparatus according to claim 4 wherein: a. said height-control means includes a manually operable control member having at least one finger piece movable in opposite directions along an adjustable path, b. said display means presents said height scale and said line of approach in an orientation such as to extend generally longitudinally of said adjustment path, c. said means forming an operative connection between said height scale and said height-control means provides for movement of said height scale in a direction to move a selected graduation mark away from said viewing point and towards said viewing point in response to alternations in the setting of said adustment means.
 7. Apparatus according to claim 1 further comprising means for varying the magnitude of the height adjustment of the shaping means produced in response to operation of the height-adjustment means for a given change of setting of the height-control means to enable the steepness of the gradients formed on said surface of said model to conform to those represented by said contour marks on said plan, or to be exaggerated or diminished as required.
 8. Apparatus according to claim 1 wherein: a. said height-control means includes means for generating a plurality of outputs representing respectively different values of height increment and scanning traverse increment ratios, b. said means for displaying indicia extending along said line of approach presents a series of graduation marks representing said different ratios respectively, c. said height-control means includes manually operable control means settable selectiveLy to provide an output representing a selected one of said ratios whereby an operator can select the ratio indicated by at least approximate coincidence between one of said graduation marks on said line of approach, and a selected contour mark intersecting said line of approach.
 9. Apparatus according to claim 1 wherein said manually operable control means comprises a keyboard including a plurality of manually operable key elements and means for indicating the particular height to scanning traverse increment ratios to which they relate respectively.
 10. Apparatus according to claim 1 wherein said means for displaying said viewing point, said portion of said plan, and said indicia comprises optical means for forming magnified images thereof.
 11. Apparatus according to claim 10 wherein said optical means includes: a. a housing extending over said cursor means, a portion of said plan adjacent thereto, and said means displaying said indicia, b. a light source in said housing for illuminating said portion of said plan, c. a display screen on which said magnified images are formed.
 12. Apparatus according to claim 1 wherein: a. said height-adjustment means includes actuating means responsive to an electrical height signal, b. said apparatus further includes reading means for generating said signal in response to playback of a record member thereby, and means for feeding said signal to said height-adjustment means, c. means are provided for correlating playback of said record member and operation of said scanning means whereby said shaping means is set to a proper height relative to said work support for each position of relative scan between said work support and said shaping means.
 13. Apparatus according to claim 11 wherein said apparatus further includes recording means including: a. means for advancing a record member through a recording station in correlation with relative scanning between said plan support means and said cursor means, b. a recording head at said station for impressing a record on said record member in response to an electrical signal, c. means for generating said electrical signal varying in dependence upon the altitude represented by said contour marks.
 14. Apparatus according to claim 11 wherein: a. said actuating means of said height-adjustment means provides stepless or continuous operation of said height-adjustment means, b. said reading means provides a height signal which is an analogue of the corresponding altitudes represented by said contour marks.
 15. Apparatus according to claim 11 wherein: a. said actuating means of said height-adjustment means provides stepwise operation of said height-adjustment means, b. said reading means provides a height signal which digitally represents the altitudes represented by said contour marks.
 16. A method of producing a three-dimensional model of a piece of terrain from data provided by a plan of the terrain bearing contour marks representative of respective altitudes, said method comprising the steps of: a. displaying in such mutual proximity to each other as to admit of concurrent viewing showing of i. a cursor means defining a viewing point ii. at least a portion of said plan iii. indicia extending along a line of approach on said portion of said plan leading to said viewing point and providing data for determining proper height adjustment of a shaping means for shaping a model blank, b. effecting relative scanning along a primary scanning path between said plan and said cursor means to cause said portion of said plan to pass said viewing point, c. viewing at least one of the contour marks intersecting said line of approach, d. effecting relative scanning along a secondary scanning path systematically relating to said primary scanning path between said model blank and said shaping means, e. positioning at least part of said data in substantial registration with at least one of said Contour marks at said viewing point and adjusting the height of said shaping means relative to said model blank in conformity with said data to form a surface on said model blank corresponding at least approximately to that represented on said plan by said contour marks.
 17. A method according to claim 16 wherein said indicia provide data as to the present height of the shaping means, and adjustment of the height of said shaping means is effected to bring about at least approximate correspondence between said indicated height and the altitude represented by the contour mark at the time when said mark passes said viewing point.
 18. A method according to claim 17 wherein the height is displayed by displaying a succession of graduation marks spaced apart in a direction longitudinally of said line of approach and effecting movement of said graduation marks collectively in correspondence with adjustment of the height of said shaping means to bring the appropriate graduation mark into coincidence with said viewing point.
 19. A method according to claim 16 wherein: a. said indicia comprises a succession of graduation marks spaced apart along said line of approach, each pertaining to a respective ratio of height adjustment to scanning increment, graduation marks situated at respectively greater distances from the viewing point defined by said cursor element pertaining to successively smaller ratios, b. scanning and height adjustment is effected by way of a series of relative scanning displacements on the one hand between said plan and said cursor means, and on the other hand between said model blank and said shaping means, accompanied in the latter case by such respective corresponding incremental adjustments of the height of said shaping means relative to said surface of said model blank as are determined by registration or approximate registration between one of said graduation marks and a contour mark of identified numerical value intersecting with said line of approach.
 20. A method according to claim 16 comprising the further step of: a. effecting relative advancement of a record member through a record station in correspondence with distance scanned along said primary scanning path, b. impressing on said record member data representing the height to which said shaping means are required to be adjusted in accordance with the altitude represented by said viewed contour marks, c. subsequently controlling relative scanning movement along said model scanning path between said model blank and said shaping means in accordance with advancement of said record member through a reading station, d. controlling the height of said shaping means with respect to said surface of said model blank in accordance with the data recorded on said record member. 